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I I I I I I I I I I I I I I I I I I I adjusted values burst event was peaks along the are shown in Table III. assumed to be the typical Front Range of Colorado. The I-hour duration cloud- storm producing flood '.~/ ~ ~ -, el->;:~~ \J~;"" ~ TABLE III Rainfall Depths One-Hour Duration Storm Va ~ ~\L(d ~ ,;)0% 2-Year 10-Year 50-Year 100-Year SOD-Year 5-Year Depth 0.62" 0.90" 1.10" 1. 60" 1.89" 2.72" The rainfall depths were then divided into 5-minute incremental values for the I-hour cloudburst event. These increments were ar- ranged into a likely storm distribution which was determined from an analysis of data in the Denver area (Reference 11). Preliminary rainfall loss rates of depression storage and in- filtration were taken from existing information. The Corps of Engineers provided a depression storage rate of 0.3 inches from their experience in studies along the Front Range. Infiltration rates were assumed to equal permeability values from the Soil Sur- vey for the Larimer County Survey Area 644, dated September 2, 1971 (Reference 12). Basin slopes and channel slopes were taken from the U.S.G.S. quadrangle maps. Channel and overbank cross sections and roughness coefficients were estimated from field inspection. The selected basin conditions for this hydrologic analysis were described in the "Scope of Work" for this contract as follows: Reach I Confluence with Cache la poudre River upstream to the north section line of Sections 29, 28, 27 and 26, Range 69 west, Township 8 North. Use fully developed basin conditions. Reach II South section line of Sections 19, 20, 21, 22 and 23, Range 69 West, Township 8 North, up- stream to the north section line at Sections 31, 32, 33, 34, 35 and 36, Range 69 West, Township 9 North. Use low density--minimum size tracts (2-5 acres) . -7-